J/ApJ/838/45 eta Carinae obs. around the 2014 X-ray minimum (Corcoran+, 2017)
The 2014 X-ray minimum of η Carinae as seen by Swift.
Corcoran M.F., Liburd J., Morris D., Russell C.M.P., Hamaguchi K.,
Gull T.R., Madura T.I., Teodoro M., Moffat A.F.J., Richardson N.D.,
Hillier D.J., Damineli A., Groh J.H.
<Astrophys. J., 838, 45-45 (2017)>
=2017ApJ...838...45C 2017ApJ...838...45C (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, X-ray
Keywords: binaries: general; stars: individual: "eta Carinae", HD 93308;
stars: winds, outflows; stars: early-type; stars: massive;
X-rays: stars
Abstract:
We report on Swift X-ray Telescope observations of Eta Carinae
(ηCar), an extremely massive, long-period, highly eccentric binary
obtained during the 2014.6 X-ray minimum/periastron passage. These
observations show that η Car may have been particularly bright in
X-rays going into the X-ray minimum state, while the duration of the
2014 X-ray minimum was intermediate between the extended minima seen
in 1998.0 and 2003.5 by Rossi X-Ray Timing Explorer (RXTE), and the
shorter minimum in 2009.0. The hardness ratios derived from the Swift
observations showed a relatively smooth increase to a peak value
occurring 40.5 days after the start of the X-ray minimum, though these
observations cannot reliably measure the X-ray hardness during the
deepest part of the X-ray minimum when contamination by the "central
constant emission" component is significant. By comparing the timings
of the RXTE and Swift observations near the X-ray minima, we derive an
updated X-ray period of PX=2023.7±0.7days, in good agreement with
periods derived from observations at other wavelengths, and we compare
the X-ray changes with variations in the HeII4686 emission. The middle
of the "Deep Minimum" interval, as defined by the Swift column density
variations, is in good agreement with the time of periastron passage
derived from the HeIIλ4686 line variations.
Description:
The most recent X-ray observations of η Car by Swift began in 2014
April. Observations were scheduled twice per week at the outset. The
Swift log of the 2014 observations discussed here is given in Table 1.
For our discussion, we also include recalibrated fluxes from Rossi
X-Ray Timing Explorer (RXTE), including previously unpublished
observations from 2010 through 2011. See section 2.
To study both orbit-dependent and non-orbit-dependent (secular)
variations, we include in Table 2 data obtained by the RXTE-PCA in the
interval 1996 February 9 through 2011 December 28. We re-reduced the
entire RXTE data set in a consistent way. See section 4.1.
Objects:
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RA (ICRS) DE Designation(s)
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10 45 03.55 -59 41 04.0 eta Carinae = * eta Car
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 88 91 Swift X-ray telescope observations
table2.dat 76 1345 Log of RXTE observations and corrected fluxes
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See also:
J/AJ/129/2018 : RXTE scaled fluxes of eta Car (Corcoran+, 2005)
J/ApJS/175/191 : Variables from 2MASS calibration fields (Plavchan+, 2008)
J/A+A/493/1093 : BVRI light curves of η Car (Fernandez-Lajus+, 2009)
J/ApJS/194/15 : CCCP: Carina's diffuse X-ray emission (Townsley+, 2011)
J/ApJ/751/73 : Equivalent widths in η Cat in 1998-2012 (Mehner+, 2012)
J/A+A/578/A122 : eta Carinae's 2014.6 spectroscopic event (Mehner+, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- ObsID Swift Observation ID
10- 19 A10 "Y/M/D" Date UT date of the Swift observation
21- 30 F10.4 d MJD [56752.7/57018.1] Modified Julian Date,
JD-2400000.5
32- 36 F5.3 d Delta [0.01/1.7] Observation length in fraction
of a day (Δ)
38- 42 F5.3 --- Phi [2.9/3.1] Phase (φ) (G1)
44- 49 F6.1 s Exp [348/5671]? Exposure time
51- 54 F4.2 10-13W/m2 Flux [0.03/3.8] Swift-XRT 2-10keV Flux,
in 10-10erg/s/cm2
56- 59 F4.2 10-13W/m2 e_Flux [0.01/1] Uncertainty in Flux
61- 65 F5.2 --- HR [-0.8/0.4] Hardness Ratio (1)
67- 70 F4.2 --- e_HR [0.02/0.2] Uncertainty in HR
72- 76 F5.2 10+22cm-2 NH [2.3/46.5] Column density (NH)
78- 82 F5.2 10+22cm-2 E_NH [0.1/83] Upper uncertainty in NH
84- 88 F5.2 10+22cm-2 e_NH [0.1/37] Lower uncertainty in NH
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Note (1): Hardness ratios calculated according to Eq. 1:
HR=(C7-C3)/(C7+C3) where C7 and C3 are the gross counts
in the 7±0.5 and 3±0.5keV bands, respectively.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Obs Observing Sequence, YYYYMMDDHH UT
17- 25 F9.3 d MJD [50122.6/55923.8] Modified Julian Date,
JD-2400000.5
27- 31 F5.3 d Delta [0.001/0.04] Observation length in fraction
of a day (Δ)
33- 38 F6.3 --- Phi [-0.4/2.6] Phase (φ) (G1)
40- 43 I4 s Exp [16/2672]? Exposure time
45- 48 F4.2 10-13W/m2 Flux [0.2/3.7] RXTE 2-10keV flux,
in 10-10erg/s/cm2
50- 53 F4.2 10-13W/m2 e_Flux [0.01/0.3] Uncertainty in Flux
55- 59 F5.2 10-13W/m2 Fluxc [-0.08/3.6] Corrected Flux,
in 10-10erg/s/cm2 (1)
61- 65 F5.2 ct/s Rate [2/37] Net count rate
67- 70 F4.2 ct/s e_Rate [0.1/2] Uncertainty in Rate
72- 76 F5.2 ct/s Bkg [10/21] Background count rate
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Note (1): Flux corrected according to Eq. 2:
Corr. RXTE Flux = (derived RXTE flux-0.314)/0.939
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Global notes:
Note (G1): φ is the time measured from the start of the X-ray minimum
divided by the period of the orbit. φ=0 corresponds well to the
start of the "Deep X-ray Minimum".
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Oct-2017